Explore the 7 basic principles of the US Constitution: popular sovereignty, limited government, checks & balances, judicial review, federalism & individual rights.

On Sept. 11, 2001, Muslim fanatics flew planes into the World Trade Center and the Pentagon, killing upward of 3,000 innocent American civilians.

Some men just age. Others evolve. These 7 uncommon principles reveal why some only get sharper, stronger, and more grounded with time.